Power amplifier with matching transformer

ABSTRACT

Aspects of a system for a power amplifier with an on-package matching transformer may include a DC/DC converter that enables generation of a bias voltage level within an IC die based on an amplitude of an input signal to a PA circuit within the IC die. The bias voltage level may be applied to a transformer, which is external to the IC die but internal to an IC package containing the IC die and/or a circuit board containing the IC package. One or more amplifier bias voltage levels, derived from the bias voltage level applied to the transformer, may be applied to the PA circuit.

CROSS-REFERENCE TO RELATED APPLICATIONS/INCORPORATION BY REFERENCE

This application is a continuation of U.S. application Ser. No.11/678,790 filed Feb. 26, 2007.

FIELD OF THE INVENTION

Certain embodiments of the invention relate to communication networks.More specifically, certain embodiments of the invention relate to amethod and system for a power amplifier (PA) chip with a matchingtransformer in the surrounding package.

BACKGROUND OF THE INVENTION

A power amplifier (PA) circuit may be biased for different modes, or“classes” of operation. Exemplary classes include Class A, Class AB, andClass B. In Class A operation, a PA may be biased such that the PA is ina conducting, or ON, state during 100% of the cycle, or the entirecycle, of the input signal. The bias level is also typically selectedsuch that the PA operates in the most linear portion of the transfercurve, which characterizes the PA circuit. In Class A operation, theoutput signal from the PA is typically a scaled version of the inputsignal, where the scaling factor is a function of the gain associatedwith the PA circuit. However, because of the bias level utilized forClass A operation, the PA is typically in a conducting state even whenthere is no input signal. Furthermore, even when the PA is amplifying aninput signal, the efficiency of the PA may not exceed 50%. For example,each watt of delivered output power, or P_(out), may require two (2)watts of delivered power, P_(DC), from a DC power supply source (such asa battery). One limitation of conventional Class A PA circuits for usein mobile wireless communication systems like wireless local areanetwork (WLAN) systems is that high bias levels often utilized to enablelarge variations in output power levels may result in unacceptably shortbattery life and/or high levels of generated thermal heat.

In Class B operation, a PA may be biased such that the PA is in aconducting state during 50%, or half, of the cycle of the input signal.This may result in large amounts of distortion of the input signal inthe output signal. In this regard, in Class B operation, the PA mayoperate in a nonlinear portion of the transfer curve. However, thetheoretical efficiency of a Class B PA circuit may reach 78.5%. Thehigher efficiency of the Class B PA results from the PA being in anon-conducting, or OFF, state half of the time. While the PA is in theOFF state, power dissipation may be theoretically zero (0). Onelimitation of Class B PA circuits is that distortion levels in outputsignals may be unacceptably high.

In Class AB operation, a PA may be biased such that the PA is in aconducting state for greater than 50%, but less than 100%, of the cycleof the input signal. In Class AB operation, the PA may be more efficientthan in Class A operation, but less efficient than in Class B operation.Furthermore, in Class AB operation, the PA may produce more distortionthan in Class A operation, but less than in Class B operation.

In Class C operation, a PA may be biased such that the PA is in aconducting state for less than 50% of the cycle of the input signal.While Class C amplifiers may produce more distortion than Class A, ClassAB, or Class B amplifiers, the theoretical efficiency of a Class Camplifier may reach 90%. The Class C amplifier may receive an inputsignal and generate a series of current pulse signals. The current pulsesignals generated by the Class C amplifier may comprise undesiredfrequency components. The output signal from the Class C amplifier maybe input to a tuned circuit, which may comprise circuitry to suppressunwanted frequency components. The resulting output signal from thetuned circuit may be a signal for which that comprises frequencieswithin a desired frequency band, for example such as a frequency bandutilized in global system for mobile (GSM) communications systems.

While the operating class of a PA provides one measure of efficiency,another measure of efficiency is determined by how efficiently theoutput power from the PA, P_(out), is delivered to a load. For purposesof the present application, this measure of efficiency may be referredto as load transfer efficiency. In a wireless communications system, anexemplary load may comprise an antenna. The PA may deliver the outputpower to the load most efficiently when the output impedance of the PAis equal to the impedance of the load. In this regard, the PA and theload may be referred to as being “impedance matched”.

Many conventional PA circuits are implemented in integrated circuit (IC)devices, or chips. The IC may comprise a die, which may comprise activeand/or passive circuitry, and a package, which may comprise a pluralityof pins, or contacts, which enable electrical conductivity betweenvarious contact points on the die, and various contact points on aboard, or other electronic assembly on which the IC is installed.

Some conventional PA integrated circuit chips achieve impedance matchingby insertion of an on-chip transformer between the output of the PA anda load, which is located off-chip. A transformer utilized for impedancematching may be referred to as a matching transformer. Because oflimitations in on-chip transformer circuits, signal energy may be lostwhen coupling a signal from the primary windings of the on-chiptransformer to the secondary windings of the on-chip transformer. Theresult may be a reduced level of delivered power to the load, P_(load).

Further limitations and disadvantages of conventional and traditionalapproaches will become apparent to one of skill in the art, throughcomparison of such systems with some aspects of the present invention asset forth in the remainder of the present application with reference tothe drawings.

BRIEF SUMMARY OF THE INVENTION

A method and system for a power amplifier (PA) chip with a matchingtransformer in the surrounding package, substantially as shown in and/ordescribed in connection with at least one of the figures, as set forthmore completely in the claims.

These and other advantages, aspects and novel features of the presentinvention, as well as details of an illustrated embodiment thereof, willbe more fully understood from the following description and drawings.

BRIEF DESCRIPTION OF SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 is a diagram of a power amplifier with dynamic biasing,on-package matching transformer, and on-die filter, in accordance withan embodiment of the invention.

FIG. 2 is a diagram of a power amplifier with dynamic biasing,on-package matching transformer, and on-package filter, in accordancewith an embodiment of the invention.

FIG. 3 is a diagram of a power amplifier with dynamic biasing, on-boardmatching transformer, and on-board filter, in accordance with anembodiment of the invention.

FIG. 4 is a flowchart illustrating exemplary steps for dynamic biasingof a PA, in accordance with an embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

Certain embodiments of the invention may be found in a method and systemfor a power amplifier (PA) chip with a matching transformer in thesurrounding package. Various embodiments of the invention may improve PAefficiency, and load transfer efficiency. PA efficiency may be improvedby dynamically changing the P_(DC) bias level in response to dynamicchanges in the amplitude of the input signal applied to the PA. Invarious embodiments of the invention, load transfer efficiency may beimproved by implementing the PA circuit in an IC die, while implementingthe matching transformer in the IC package surrounding the die. Byplacing the matching transformer in the IC package, materials may beutilized with higher permeability, and lower parasitic resistance and/orcapacitance values. The result may be a transformer, for which lesssignal energy may be lost which coupling a signal from the primarytransformer winding to the secondary transformer winding. Thedynamically changed P_(DC) bias level may be applied to the matchingtransformer, which may in turn enable dynamic biasing of the PA circuit.In various alternative embodiments of the invention, the matchingtransformer may be located in a board on which the IC may be installed.

FIG. 1 is a diagram of a power amplifier with dynamic biasing,on-package matching transformer, and on-die filter, in accordance withan embodiment of the invention. Referring to FIG. 1, there is shown aboard 102. The board 102 may comprise an IC package 104. The IC package104 may comprise a die 106, a matching transformer 108, and an antenna110. The die 106 may comprise a DC to DC (DC/DC) converter 112, a lookup table (LUT) 114, an envelope detector 116, a current source 118,transistors 120 and 122, and a filter 124. In an exemplary embodiment ofthe invention, the transistors 120 and 122 may be fabricated byutilizing CMOS technology.

The package 104 may comprise a plurality of pins, or other contactpoints, each of which may enable electrical conductivity from a contactpoint on the die 106, to a contact point on the board 102. The package104 may utilize any of a variety of technologies for enclosing a die106.

Within in the die 106 the DC/DC converter 112 may comprise suitablelogic, circuitry and/or code that may enable conversion of an inputsupply voltage, V_(DD), to a bias voltage, V_(Bias), based on an inputcontrol signal, Supply Control. The voltage level for the bias voltageV_(Bias) may be less than or equal to the voltage level of the inputsupply voltage V_(DD). In an exemplary embodiment of the invention, theDC/DC converter 112 may comprise a switching regulator circuit.

The envelope detector 116 may comprise suitable logic, circuitry and/orcode that may enable detection of an amplitude of a time varying inputsignal, labeled as the differential signal LO+ and LO− in FIG. 1. Basedon the detected amplitude of the input signal, the envelope detector 116may enable representation of the detected input signal amplitude in agenerated output signal labeled Amplitude in FIG. 1. In variousembodiments of the invention, the signal Amplitude may be an analogsignal and/or a digital signal.

The LUT 114 may comprise suitable logic, circuitry and/or code that mayenable generation of a Supply Control code word based on an inputAmplitude signal. In an exemplary embodiment of the invention, the LUT114 may comprise one or more memory circuits that utilize the Amplitudesignal to generate an address to access a memory location. Based on thebinary data retrieved from the address memory location, the SupplyControl code word may be generated.

The current source 118 may comprise suitable logic, circuitry and/orcode that may enable generation of a current, I_(Bias).

The transistors 120 and 122 may form a differential power amplifier (PA)circuit 123 that receives a differential input signal, labeled LO+ andLO−, and generated an amplified output signal at the nodes labeled D₁and D₂. The input LO+ may be applied to the gate of the transistor 120,and the input LO− may be applied to the gate of the transistor 122. Thenode D₁ may be coupled to the drain of the transistor 120, and the nodeD₂ may be coupled to the drain of the transistor 122.

The filter 124 may comprise suitable logic, circuitry and/or code thatmay suppress signals within one or more specified frequency ranges. Inan exemplary embodiment of the invention, the filter 124 may comprise abandpass filter that may suppress frequency components in thedifferential signal at the nodes D₁ and D₂, which are outside of a passband for the filter 124.

The matching transformer 108 may comprise primary windings labeled P₁,P₂ and P₃ in FIG. 1, and secondary windings labeled S₁ and S₂. Theprimary and secondary windings may comprise electrically conductingmaterial, such as wire manufactured from a suitable metal or conductor,and a core manufactured from a suitable magnetically permeable material.The location of the matching transformer 108 in the package 104 mayenable the utilization of materials, which may not be utilized for themanufacture of matching transformers, which are located on a die. Inaddition, the location of the matching transformer 108 in the package104 may enable the realization of physical dimensions, which may not beachievable for matching transformers, which are located on a die. Thecombination of wider material choice, and wider choice of physicaldimension, may enable more efficient transfer of signal energy from theprimary windings to the secondary windings in the matching transformer108, than may be achievable with matching transformers, which arelocated on a die.

In an exemplary embodiment of the invention, the package 104 may be aflip chip package, containing the matching transformer 108 and antenna110, to which the die 106 may be bonded. A contact point for the drainof transistor 120, labeled D₁ in FIG. 1, may be coupled to a contactpoint for the primary winding of the matching transformer 108, labeledP₁ in FIG. 1. A contact point for the drain of transistor 122, labeledD₂ in FIG. 1, may be coupled to a contact point for the primary windingof the matching transformer 108, labeled P₃ in FIG. 1. A contact pointfor the output of the DC/DC converter 112 may be coupled to a contactpoint for the primary winding of the matching transformer 108, labeledP₂ in FIG. 1. A contact point for the secondary winding of the matchingtransformer 108, labeled S₁ in FIG. 1, may be coupled to the antenna110. A contact point for the secondary winding of the matchingtransformer 108, labeled S₂ in FIG. 1, may be coupled to ground.

In operation, a dynamic bias level for the PA 123 may be determinedbased on a differential input signal LO+ and LO−, which may be appliedto the gates of transistors 120 and 122, respectively. The amplitude ofthe differential input signal may be detected by the envelope detector116. The envelope detector 116 may represent the detected differentialinput signal amplitude via the signal, Amplitude. The LUT 114 maygenerate a Supply Control signal based on the Amplitude signal. TheDC/DC converter 112 may convert the supply voltage V_(DD) to a biasvoltage V_(Bias) based on the Supply Control signal. The bias voltagemay be applied to the matching transformer 108 at the point labeled P₂.In response, the bias voltage may be applied to the drain of thetransistor 120, via the contact point D₁, and the drain of thetransistor 122, via the contact point D₂. The bias voltage applied atthe contact point D₁ may provide a bias voltage to the transistor 120while the bias voltage applied at the contact point D₂ may provide abias voltage to the transistor 122.

In various embodiments of the invention, the LUT 114 may enable the PA123 to operate in various classes. For example, the LUT 114 may enablethe dynamic selection of bias levels V_(Bias), which enable thetransistors 120 and 122 to operate in the linear portion of therespective transfer curves for the given amplitude of the differentialinput signal LO+ and LO−, such as in a Class A amplifier. The dynamicbiasing method, however, may enable the PA 123 to operate with increasedefficiency compared to conventional Class A amplifier designs becausethe bias level, and power consumption of the PA 123, may be increasedand/or decreased in response to the amplitude of the differential inputsignal. Alternatively, the LUT 114 may enable the dynamic selection ofbias levels, which enable the PA 123 to operate as a Class B amplifier,a Class AB amplifier, or a Class C amplifier, for example.

The output voltage from the PA 123, V_(out), may be measured between thenodes D₁ and D₂. The corresponding output current, as supplied via theDC/DC converter 112, may be I_(Bias). The output power from the PA 123,P_(out), may be proportional to the multiplicative productV_(out)·I_(Bias). The matching transformer 108 may transfer the outputpower from the PA 123, P_(out), measured at the primary windings betweennodes P₁ and P₂, and transfer at least a portion of P_(out), P_(load),to the secondary windings as measured between the nodes S₁ and S₂. Theportion of power which may be transferred from the primary windings tothe secondary windings depends upon signal energy loss between theprimary windings and secondary windings of the matching transformer 108,P_(loss), as shown in the following equation:P _(load) =P _(out) −P _(loss)  [1]

In various embodiments of the invention, the matching transformer 108may be located within the package 104 as opposed to being located withinthe die 106. Locating the matching transformer 108 external to the die106 may enable implementation of more efficient matching transformerdesigns for which signal energy loss may be lower in comparison to someconventional IC designs in which the PA 123 and matching transformer arelocated within an IC die. The matching transformer 108 may realize thehigher efficiency by utilizing high permeability core materials and/orlow resistance, low parasitic parameter materials for the primary andsecondary windings. In various embodiments of the inventionP_(load)≈P_(out).

The voltage V_(out) may induce a proportional voltage, V_(A), across thesecondary windings of the matching transformer as measured at nodes S₁and S₂ respectively. The voltage V_(A) may correspond to a voltageapplied to the antenna 110. The antenna 110 may correspond to a loadimpedance, R_(L). Similarly, the current I_(Bias) may induce aproportional current, I_(load), through the load impedance R_(L).Consequently, the voltage V_(A) may be proportional to the currentI_(Bias), while the power transferred to the antenna, P_(load), may beproportional to I_(Bias) ².

Changes in the voltage level for V_(out) may result in correspondingchanges in the current level for I_(Bias). In turn, this may result incorresponding changes in the voltage level for V_(A). For some ICfabrication technologies, such as CMOS, the impedance of the transistors120 and 122 may be relatively small (as measured in ohms). In addition,the technology may require that changes, or swings, in the voltagelevels for V_(out) be limited. By contrast, the impedance of the antenna110, may be considerably larger, for example R_(L)=50 ohms. By utilizingthe matching transformer 108 to provide impedance matching between theimpedance of the PA 123, as measured between the nodes D₁ and D₂, andthe impedance of the antenna 110, R_(L), voltage level swings in V_(out)may be limited.

FIG. 2 is a diagram of a power amplifier with dynamic biasing,on-package matching transformer, and on-package filter, in accordancewith an embodiment of the invention. Referring to FIG. 2, there is showna board 102. The board 102 may comprise an IC package 204. The ICpackage 204 may comprise a die 206, a matching transformer 108, a filter224, and an antenna 110. The die 206 may comprise a DC to DC (DC/DC)converter 112, a look up table (LUT) 114, an envelope detector 116, acurrent source 118, and transistors 120 and 122.

FIG. 2 differs from FIG. 1 in that FIG. 2 shows an exemplary embodimentof the invention in which the on-die filter 124 from FIG. 1 is replacedby an on-package filter 224 in FIG. 2. The on-package filter 224 iscoupled to the nodes P₁ and P₂ as is the on-die filter 124 in FIG. 1.The function and operation of the on-package filter 224 may besubstantially similar to the on-die filter 124.

FIG. 3 is a diagram of a power amplifier with dynamic biasing, on-boardmatching transformer, and on-board filter, in accordance with anembodiment of the invention. Referring to FIG. 3, there is shown a board302. The board 302 may comprise an IC package 304. The IC package 304may comprise a die 206, a matching transformer 308, a filter 324, and anantenna 310. The die 206 may comprise a DC to DC (DC/DC) converter 112,a look up table (LUT) 114, an envelope detector 116, a current source118, and transistors 120 and 122.

FIG. 3 differs from FIG. 3 in that FIG. 3 shows an exemplary embodimentof the invention in which the on-package filter 224 from FIG. 2 isreplaced by an on-board filter 324 in FIG. 3, the on-package matchingtransformer 108 from FIG. 2 is replaced by an on-board matchingtransformer 308, and the on-package antenna 110 from FIG. 2 is replacedby an on-board antenna 310. The function and operation of the on-packagefilter 224 may be substantially similar to the on-die filter 124, theon-board matching transformer 308 is substantially similar to theon-package matching transformer 108, and the on-board antenna 310 issubstantially similar to the on-package antenna 110.

FIG. 4 is a flowchart illustrating exemplary steps for dynamic biasingof a PA, in accordance with an embodiment of the invention. Referring toFIG. 4, in step 402 the envelope detector 116 may detect the amplitudeof the differential input signal to the PA 123. In step 404, theenvelope detector 116 may send a signal to the LUT 114, which indicatesthe amplitude of the differential input signal. In step 406, the LUT 114may generate supply control bits based on the input amplitudeinformation received in step 404. In step 408, the DC/DC converter 112may dynamically set a bias voltage level for V_(Bias), based on thesupply control bits received in step 406. The magnitude of the biasvoltage level may be less than or equal to the magnitude of the supplyvoltage level V_(DD).

In various embodiments of the invention, the bias voltage level may becontinuously set dynamically during circuit operation in response tochanges in the amplitude of the differential input signal to the PA 123.In this regard, step 402 may follow step 408.

Aspects of a system for a power amplifier with an on-package matchingtransformer may include a DC/DC converter 112 that enables generation ofa bias voltage level within an IC die 106 based on an amplitude of aninput signal to a PA circuit 123 within the IC die 106. The bias voltagelevel may be applied to a transformer 108, which is external to the ICdie 106 but internal to an IC package 104 containing the IC die 106and/or a circuit board 102 containing the IC package 104. One or moreamplifier bias voltage levels, derived from the bias voltage levelapplied to the transformer 108, may be applied to the PA circuit 123. Asubsequent bias voltage level may be dynamically generated based on asubsequent amplitude of the input signal to the PA circuit 123.

The generated bias voltage level may be selected based on a look uptable 114. The look up table 114 may enable the PA circuit 123 tooperate as a Class A amplifier, a Class B amplifier, a Class ABamplifier, and/or a Class C amplifier. The output signal from the PAcircuit 123 may be applied to the primary windings of the transformer108. The transformer 108 may enable generation of a secondary outputsignal at the secondary windings based on the output signal applied tothe primary windings. The transformer 108 may enable matching of anoutput impedance from the PA circuit 123 measured at the primarywindings to an impedance load measured at the secondary windings. Theimpedance load may comprise an antenna 110.

A filtering circuit 124 may be applied to the output signal from the PAcircuit 123. The filtering circuit may be internal to the IC die 106,the IC package 104, and/or the circuit board 102. The filtering circuit124 may be a bandpass filter.

Accordingly, the present invention may be realized in hardware,software, or a combination of hardware and software. The presentinvention may be realized in a centralized fashion in at least onecomputer system, or in a distributed fashion where different elementsare spread across several interconnected computer systems. Any kind ofcomputer system or other apparatus adapted for carrying out the methodsdescribed herein is suited. A typical combination of hardware andsoftware may be a general-purpose computer system with a computerprogram that, when being loaded and executed, controls the computersystem such that it carries out the methods described herein.

The present invention may also be embedded in a computer programproduct, which comprises all the features enabling the implementation ofthe methods described herein, and which when loaded in a computer systemis able to carry out these methods. Computer program in the presentcontext means any expression, in any language, code or notation, of aset of instructions intended to cause a system having an informationprocessing capability to perform a particular function either directlyor after either or both of the following: a) conversion to anotherlanguage, code or notation; b) reproduction in a different materialform.

While the present invention has been described with reference to certainembodiments, it will be understood by those skilled in the art thatvarious changes may be made and equivalents may be substituted withoutdeparting from the scope of the present invention. In addition, manymodifications may be made to adapt a particular situation or material tothe teachings of the present invention without departing from its scope.Therefore, it is intended that the present invention not be limited tothe particular embodiment disclosed, but that the present invention willinclude all embodiments falling within the scope of the appended claims.

What is claimed is:
 1. A system comprising: at least one circuit thatproduces a generated bias voltage within an integrated circuit (IC),said generated bias voltage being continuously varied in response tochanges in an amplitude of an input signal to a power amplifier; said atleast one circuit enables application of said generated bias voltage toa transformer internal to an IC package containing said IC; said atleast one circuit enables application of an amplifier bias voltage tosaid power amplifier wherein said amplifier bias voltage is derived fromsaid generated bias voltage applied to said transformer.
 2. The systemof claim 1, wherein said at least one circuit enables selection of saidgenerated bias voltage from a look up table.
 3. The system of claim 2,wherein said look up table enables said power amplifier to operate asone or more of a Class A amplifier, a Class B amplifier, a Class ABamplifier and/or a Class C amplifier.
 4. The system of claim 1, whereinsaid at least one circuit enables application of an output signal fromsaid power amplifier circuit to primary windings of said transformer. 5.The system of claim 4, wherein said at least one circuit enablesgeneration of a secondary output signal at secondary windings of saidtransformer based on said output signal applied to said primarywindings.
 6. The system of claim 5, wherein said at least one circuitenables matching of an output impedance from said power amplifiermeasured at said primary windings to an impedance load measured at saidsecondary windings.
 7. The system of claim 6, wherein said impedanceload comprises an antenna.
 8. The system of claim 4, wherein said atleast one circuit enables application of a filtering circuit to saidoutput signal.
 9. The system of claim 8, wherein said filtering circuitis internal to said IC package.
 10. The system of claim 8, wherein saidfiltering circuit is a bandpass filter.
 11. A method comprising:producing a generated bias voltage within an integrated circuit (IC),said generated bias voltage being continuously varied in response tochanges in an amplitude of an input signal to a power amplifier;applying said generated bias voltage to a transformer internal to an ICpackage containing said IC; applying an amplifier bias voltage to saidpower amplifier wherein said amplifier bias voltage is derived from saidgenerated bias voltage applied to said transformer.
 12. The method ofclaim 11 further comprising selecting said generated bias voltage from alook up table.
 13. The method of claim 12, wherein said look up tableenables said power amplifier to operate as one or more of a Class Aamplifier, a Class B amplifier, a Class AB amplifier and/or a Class Camplifier.
 14. The method of claim 11 further comprising applying anoutput signal from said power amplifier circuit to primary windings ofsaid transformer.
 15. The method of claim 14 further comprisinggenerating a secondary output signal at secondary windings of saidtransformer based on said output signal applied to said primarywindings.
 16. The method of claim 15 further comprising matching of anoutput impedance from said power amplifier measured at said primarywindings to an impedance load measured at said secondary windings.